A modem electronically-controlled sorting machine as used for sorting products in the fruit and vegetable industry has three main elements:                1) a conveyor for presenting the product to the vision system,        2) a vision system which views and inspects the product and makes the necessary decisions to accept or reject product, and        3) a rejection device which kicks out the “rejected” product.        
Such arrangements are typically used in processing factories or on harvesting machinery in the field.
Currently, when the vision system identifies an object to be rejected, it sends an electronic signal to the rejector telling it for example “to activate finger no. 34 to reject the tomato which is traveling in its direction at a predetermined period of time”.
The rejection device consists of a bank of electro-pneumatic finger/cylinders. There are typically 40-60 fingers (ejectors) across the width of the conveyor, wherein the normal ejector width is 25 mm.
Each ejector comprises an arrangement of pneumatic components connected to a mechanical paddle or solid member. The paddle is activated to achieve product (typically whole fruit and vegetable) ejection from an in-flight product stream.
Typically, the pneumatic components comprise electro-pneumatic valves such as mass-produced 4-way valves and off-the-shelf single-acting or double-acting cylinders. Whilst improvements have been made to the vision system, few improvements have been made to the rejection device. The efficiency of the rejection device is limited by the efficiency of the major proprietary parts of such valves, cylinders etc.
The actuators to which the present invention applies are of compact dimensions, the diameter of the cylinder of the unit being typically less than 25 mm to match the width of the ejector finger or paddle. The overall length of the actuating device is then typically of the order of 150 mm approximately, so that a bank of for example 60 actuators can be readily accommodated in convenient manner in driving association with the fingers, while also being accessible for maintenance and replacement. Because of their relatively compact dimensions, the units of the invention have a relatively small air volume or capacity, while the moving parts are also relatively light in weight, so that inertia effects are minimised and rapid action is facilitated.
Deficiencies of the aforementioned known systems include                1) Inconsistency of response time from mass produced 4-way valves,        2) Cost of “balanced” 4-way valves,        3) Limitations caused by the cycle time with a conventional 4-way valve,        4) Limitations on the forces which can be generated in the cylinder by the conventional 4-way valve,        5) Low ejector speeds,        6) Slow response times, and        7) Damage to rejected product.        